Microservices Interview Questions

• Monolith vs microservices trade-offs? Monolith: simpler dev/deploy, one DB, lower latency. Micro: independent scaling/deploy, tech diversity, team autonomy — but distributed systems complexity, network overhead, operational burden

• How do you handle distributed transactions? Saga pattern (choreography or orchestration) with compensating transactions. Avoid 2PC — it's slow and creates tight coupling

• How to ensure data consistency across services? Eventual consistency via events. Outbox pattern for reliable publishing. Idempotent consumers (deduplicate by event ID)

• What is the circuit breaker pattern? Stops calling a failing downstream service after threshold; enters open state. After timeout, half-open state tests if service recovered. Implemented by Resilience4j (Java), opossum (Node)

• How do you handle service discovery? Client-side (Eureka) or server-side (AWS ALB, Kubernetes service DNS). In K8s, services resolve by name: http://user-service:3001

• How do you propagate auth across services? Pass JWT in Authorization header between services. API Gateway validates token; downstream services trust the gateway or re-verify the token

• How to debug distributed systems? Distributed tracing (OpenTelemetry, Jaeger, Zipkin) — propagate trace ID across all service calls. Centralized logging with correlation IDs

• When NOT to use microservices? Early-stage products (YAGNI), small teams, tight deadline. Start with a modular monolith; extract services when boundaries are clear and scaling needs justify complexity